Cycloalkane oxidation



Patented Mar. 18, 1952 UNITED STATES PATENT OFFICE Francis T. Wadsworth,Dickinson, Tex., assignor to. Pan American Refining Corporation, TexasCity, Tex., a corporation of Delaware No Drawing. Application May '26,r950, Serial .No. 164,603

1 This invention relates to a catalytic process for the oxidation ofcycloalkanes to produce principally alkane dicarboxylic acids. Moreparticularly, this invention relates to a catalytic process for theoxidation of cyclohexane'wi th added molecular oxygen in the presence ofa reaction medium and solvent consisting essentially of acetone.

In processes for the oxidation of cycloa'llranes 10 containing 4 to 6carbon atoms, inclusive, in the ring by means of oxygen and a polyvalentheavy metal catalyst, the use of a reaction solvent was found to beessential in order to procure comf mercially significant yields of thedesired alkane dicarboxylic acids. This has been found to beparticularly true in processes of the above-men tioned type when appliedto the oxidation of cyclohexane to produce alkane dicarboxylic acids,particularly adipic acid. When cyclohexane is oxidized in the presenceof soluble co balt and/or manganese carboxylates in the absence of areaction solvent, even the employment of severe operatingconditions'leads to the production of cyclohexanol, cyclohexanone, and

combustion products such as C0, C02 and water,

Atmospheric Pressure (ll-5 0,)

Liquid Vapor Phase Phase rim-Stainless Steel 0. 082 0. 013 309-StainlessSteel 0. 010

3 i7 Stainless Steel i 410-Stainless SteeL. 0.022 lilo-Stainless Steel0.001 HaStelloy-A, 0. 050 .Hastelloy-B 0. 005 Hastelloy-O. A1, 38-1-11 1i Acetic acid 15 even more corrosiv hen employed under moderate oxygenpressures such as are used in processes of the above-described type.Thus, at a temperature of mil-105 C. and .150

' p. s. i. g. air pressure, the corrosion rate of but not to theformation of adipic acid. When cyclohexane is oxidized in solution .inbutyl acetate in the presence of polyvalent heavy metal carboxylatecatalysts, essentially the same oxidation products are obtained as whenno solvent whatever is employed; when glacial acetic acid is substitutedas the solvent, adipic acid is produced. The solvent plays an importantrole in productionof adipic acid in processes for the.

oxidation of cyclohexane with air or oxygenfin the presence of sclublepolyvalent metal salts, its use is 4 nevertheless attended by certainserious disadvantages? Although acetic acid is not generally consideredto be a highly corrosive medium, it"a'ctually becomes an extremelycorrosive medium under the conditions emp'loyediin oxidation processesof the type above described. Aerated acetic acid is a highly corrosivemedium even at atmospheric pressure and 115 C.,- as

shown by-theiollowingcorrosion rates, given as I W I a. additionalcbjectof this invention .is; to provide a.

liquid phase.

Hastelloy-C is increased to 0.0027 I. P. Y. in the At the higher partialpressures of oxygen normally employed in the catalytic oxidation ofcycloalkanes, for example, oxygen partial pressures of about 100 to 300p. s. i. .g.,,

' lum, special stainless steels and the like.

"The known processes for the oxidation of cycloalkanes to alkanedicarboxylic .acids invariably yield intermediate oxidation products,particularly cycloalkanols and cycloalkanones.

When glacial acetic acid is employed .as the reaction solvent,=cycloalkanols are .not recoverable as such from the reaction mixture,but principal- 1y" as cycloalkanol acetates." The recovery of theseesters and their treatment to regenerate the cycloalkanol andv aceticacid, respectively, constitute further problems and deficienciesconnected with the employment of glacial acetic acid as the reactionsolvent inprocesses of cycloalkane oxidation.

One object of this invention is to provide a novel solvent for use inthe oxidation of cycloalkanes to produce principally alkane dicargbjo'xylic acids.

' is to provide a novel solvent for use in the oxidation of cyclohexane,cyclopentane, cyclobutane Another object of this invention lysts to.produce 'alkane dicarboxylic'facids. An

process for the oxidation of cyclohexane in solution in a solventconsisting essentially of acetone in the presence of certain heavy metalcatalysts to produce substantial yields of adipic acid, together withcyclohexanol and cyclohexanone. Yet another object of my invention is toprovide a novel combination of acetone solvent and manganese and cobaltadipates for employment in the oxidation of cyclohexane to produceadipic acid, cyclohexanol and cyclohexanone. These and other objects ofmy invention will become apparent from the ensuing description thereof.

The process of this invention will be described principally by referenceto theoxidation of cyclohexane, although it should be understood that itmay likewise be applied to other 'cycloalkanes containing 4 to 6 carbonatoms, inclusive, in the J ring or to their methylor ethyl-substitutionproducts. It will also be apparent that the process of the presentinvention is not limited to the employment of substantially purecycloalkane charging stocks, but may likewise be ap plied to natural orsynthetic cycloalkane-containing fractions, particularly to suchfractions which are derived from petroleum, or from synthesizingoperations appliedto petroleum frac-. tions, for example,Friedel-Crafts-catalyzed isomerization of methylcyclopentane fractionsto cyclohexane.

Briefly, the process of the present invention comprises the oxidation ofa solution of cyclohexane in acetone, the latter-being present inamounts ranging from about 10 to about weight percent, based on themixtureof acetone and cyclohexane, in the presence of a solu lepolyvalent heavy metal oxidation catalyst of the type-of manganese,cobalt and copper; oil-soluble salts, for example acetates,naphthenates, oleates;

adipates, etc., of the aforementioned and similar heavy metals, ormixtures of oil-solublesalts of manganese, cobalt, copper and the like.The catalyst concentration in the reaction mixture can be varied betweenabout 0.001 and about 0.1 percent by weight (calculated as metal), andis preferably selected between about 0.015 and'about 0.033 percent byweightjbased upon the, weight of the cycloalkane charging stock. Theprocess is eflected at temperatures between about and about 1 l0 0.,preferably between about C. and about C., employing oxygenipartia lpressures between about 100 and about 300 p.-s. i. g., preferably aboutto a bout 225 p. s. i. g. The reaction period may vary between about 1and about 8 hours, but is preferably selected in about the 2 to 4 hourrange.

It is highly surprisingto find that acetone could be employed as thereaction solvent in cycloalkane oxidation processes, since acetone isknown to be readily oxidizable when treated with oxygen in the presenceof polyvalent heavy metal oxidation catalyst. inthe presence of aceticacid. Acetone oxidizes under these conditions with re-" markable easein'the absence of a 'c'ycloalkane (note Examples 3 and 4 of U. S. Patent2,005,183;

roomtemperature, whereupon unreacted cyclohexane formed a supernatantlayer, which was decanted. The lower layer of reaction products wasdistilled under a pressure of 200 mm. of mercury and the resultantdistillate was redistilled at atmospheric pressure, with the resultsshown in the following tabulation.

Vol. Percent Distilled The atmospheric boiling point of acetone is 56 C.

It will, therefore, be apparent that acetone must have oxidizedcompletely under the conditions employed in the oxidation reaction,since no trace of it was found in the reaction products. The operationyielded 11.1 weight percent of. adipic acid, based on the cyclohexanecharged.

with an ultimate conversion of 36.9 weight percent of the charge toadipic acid.

In marked contrast, as'will be shown in detail, hereinafter,. I havefound thatwh'en, acetone. is employed as the sole reaction solvent, inthe.

absence of acetic acid, substantiallyno acetone oxidation occurs inthepresence of a cycloalkane charging stock, butinstead. selectiveoxidation of the cycloalkane occurs to. produce a commerciallydesirableyield of alkane'dic'arboxylic acid, ac-

companied by cycloalkanoneand free cycloalkanol. More particu1arly', Ihave vdiscovered'that the oxidation of cyclohexane in asolventconsisting essentiallyof acetone in the presence of.

certain soluble polyvalent heavy metal salts. proceeds smoothly toproduce commercially attractive yields of adipic acid, cyclohexanol andcyclohexanone. I have found acetone to be resistant to oxidationunderthese conditions and readily recoverable from the resultantreaction mixtures. Thus, in the oxidation of cyclohexane in solution inacetone to produce adipic acid, I have found that the total distillatefrom a typical operation contains acid equivalent only toabout 0.65percent acetic acid. Acetone recoveries of 95-97 percent and even morecan be obtained. .1 have, moreover, discovered that the influence ofacetone upon cyclohexane oxidation is specific and that other ketonessuch as diphenyl ketone do not exert this influence.

In. order to afiord specific illustrations of the process of the presentinvention and without the intention of'unduly limiting the scopethereof,run data are set forth in the following table. Small proportions ofcyclohexanone, as-shown, were employed in these runs as .a reactioninitiator, i. e. as a material which served to reduce the. ratherextended induction period before the onset of reaction which wouldotherwiselbe ex peri'enced. .I have found that acetone doesno't,function as an initiator in the catalytic oxidation of cyclohexane.

The inability of acetone to function as a re-i action initiator isdemonstrated by the followingexperiment- A mixture of 61 g.- ofcyclohexane, 35%. purity),v 3.8.5 'L'g.ffof..acetone and 0.07. -g each,of cobalt, mangai'i'eseandcopper acetates: was treated with oxygenat"a"p'artial p'r'essiiretr tone solvent. In run 3 a mixture ofmanganese 7f 5 200 p. s. i. g. for 3 /2 hours at temperatures between126 and132 C. without evidence of. .any

varies from about 45 to 19.0 minutes.

the corresponding acetates the induction l able I j Adipic Acid YieldsWeight Per I Cyclo- Ace- Cent Ace Cam] i Cyclo- Oxygen v ys wewnt Temp,Time, Run tone tone in per cent 0110:1311 v hexanqne C. hrs. Weight perg i gg E Mixture cent (Jon verted Charge Charge 61.7 1 49. 44. 5 Mnacetate-0.162;... 0.95 130-132 200 4 11. 5

61. 7 49. 5 44. 5 1819 acetititeilliilio. 0. Q5 130-132 I 200 4 9. .8

name a e 61.7 49.5 44.5 gl fi i 3b 0. 95 130-132 200 4 12.3 n ace a e 4l7. 4 7t 9. 2 g? g 5 130 200 I 47 6. 9 I 48. 7

n ace a e .1 i l 5... 77.7 137 26.2 {commw0162 9.5 13,0 200 4. 15.2 6,61. 7 49. G 44. 5 C11 acetate-0.162 0.95 130-132 2.00 4 2 I I Mnacetate-0.162 V 7 61. 7 49. 5 4445 80 cet al egl gau- 0. .95 I 130-132200 4 11.9 uaceac Mn adipates0.l97 1 U s 543 239 g b 5.4 127-132 150 017.2 53.0

I 1 11a ipa es .7 9.-,.. 46s 31 L0 gg z 96 3 4.7 I 127-132 150 6 11.149.2

. na ipa es .1 7 10 381 39s .50 E4 z b g7 3.8 121-132 150 s 1 1.8 513.5

. naipaes.l -i I 11 545 130 20.2 g g 5.4 127-132 200 6 l6 37.4

naipees a 12 545 19s 26. a, 4 adpatgsfiol 92 5. 4 127-132 200 6 17. 5 00naipaes0.l 13 46b 31, 40.5 g 96 59 4. 7 127-122. 200 e 21. 5 44. 3 .1naipaes'.l 14 330 396 to. 5 g fi} 3.8 127-132 200 t 22 46.2

inaip es. 7.. .545 130 20.2 i g 5.4 127-132, 250 c 21.9 42.6 naipaes -D238 30.5 fg7 u. 4 127-132 250 .5 1 28. 4 r :17. U

1 na ipates 466 317 40. 5 gf i bfigi- 4. 7 127-132 250 s 26.6 .19. 2

na rpa es- 389 096 50.5 I{ as 127-132 250 s 29.2 46.3

oxygen absorption (drop in pressure) whatsoever. The reaction bomb wasthen opened and 0.95 g. cyclohexanone was added to the reaction mixture.The reaction bomb was then repressured with oxygen, reheated to reactiontemperature and it was found that the pressure began to drop about .20minutes after the bomb reached reaction temperature. The yield of adipicacid recovered was 3 weight percent, based on the cyclohexane charged.It should be pointed out that the recovery was somewhat inefficient, sothat the true yield of adipic acid was somewhat higher.

Referring to the table, the reported adipic acid yields are based solelyupon adipic acid filtered from the reaction mixture. It should be bornein mind that additional adipic acid can readily be produced from theinitial filtrate.

Run 1 demonstrates the applicability of manganese acetate and run 2 ofcobalt acetate as catalysts for the oxidation of cyclohexane in theaceand cobalt acetates was employed. In runs 4 and 5 manganese-cobaltacetatecatalysts were employed atfreducedacetone concentrations.

.Run 6 indicates that copper acetate is a less active catalyst thancobalt and manganese ace- 5 tates under comparable conditions, but run'7 indicates that copper acetate can be employed together with bothmanganese and cobalt acetates. Manganese-and cobalt adipate catalystswere employed in runs 8 to 18, inclusive. The adipate salts-sworeprepared by heating a mixture of cobait and manganese acetates withadipic acid for 1 3-4 minutes at 130-140 C. The adipic acid employed inpreparing the cobalt and manganese j adipates was an adipic acidfiltrate from a previous oxidation run. The adipic acid filtrate a1-verted cyclohexane and water as distillate.

8 to 10 inclusive, were conducted ath ipartial oxygen pressure of p. s.i. g., with acetone concentrations varying between BOand 50 weightpercent of the cyclohexane-acetone, mix,-

ture. is'that the extent of cy-ciohexane conversionper pass decreasessomewhat. with increasing cy l hexane dilution. but that a somewhathigher The trend discernible from this variation adipic acid yield isobtainable .at increased dilutions.

mixture can be more or less ofi'set by employing increased oxy enpartial pressures (200 'p. s. i. g..), whereuponincreased adipic acidyields, based on charge, are obtained, but the ultimate yield of adipicacid is somewhat reduced.

. Runs 15 to 1 inclusive, illustrate-the fact that atqrelatively highoxygen partial pressure (250 p. s. i. g), relatively dilute reactionsystems can be employed and a high adipic acid yield per pass withoutundue ultimate adipic acid. yield losscan be obtained.

It should be nnderstoodthatconventionalsep ration techniques, can be,employed in -=connecticn withjthe processoi my invention. 'Oneconventional procedure which I have employed following batch operationof the present oxidation process is to distill the reaction mixture to abottoms temperature of 141 C. to remove acetone, uncon- The distillationresidue is then cooled to -18 C.'to crystallize adipic acid, which isthereafter separated by filtration. The adipic acid filtrate can bereadily oxidized, for example, with nitric acid, to yield additionaladipic acid. A typical adipic acid filtrate was found to analyze asfollows.

I Weight per cent of filtrate Qyclohexanol-cyclohexanone 26 Adipicacid--- 23 l ligher molecular weight acid 51 period carried out with 40percent nitric acid at 50-55 C.

in the presence of a trace of copper, the nitric acid beingreduced inthis step to N20. In the second step-the temperature was raised to 600., at which it was maintained for 1 to 1.5 hours while the nitric acidwas reduced to N02. The total reaction time in both steps was 2-2.5hours. It was found that the yields of adipic acid, based on the adipicacid filtrate of runs 8, 9 and 10, were 85.5, 88.0 and 80.0 weightpercent, respectively. The overall adipic acid yields in runs 8, 9 and10 were, thus, 29.7, 26.0 and 20.5 mol percent, based on cyclohexanecharged, and 77.8, 81.5 and 86.0 mol percent, based on the cyclohexaneconverted.

In a study of the use of "ketones other than acetone for the oxidationof cyclohexane toadipic acid, an oxidation was carried out in which g.of benzophenone (diphenylketone) Were used as the solvent for 62 g. ofcyclohexane. Catalysts consisting of cobalt acetate, manganeseacetate,copper acetate (.01 g. each) and 1 percent cyclohexanone were used. Areaction period of 4 hours at 125-130" C. and an oxygen pressure of100-250 p. s. i. g. were used. Only a slight drop in oxygen pressure wasnoted, with a 3 weight percent yield of adipic acid, based on thecyclohexane charged, being recovered. It is obvious that-benzophenone isnot equivalent to acetone.

Having thus described my invention, what I ence of a polyvalent heavymetal catalyst and cyclohexanone reaction initiator, the improvementwhich comprises effecting said oxidation in a solution of cyclohexane ina solvent consisting essentially of acetone, the proportion of acetonein said solution being between about 10 and about '70 ercent by weight.

3. In a process for the liquids-phase oxidation of cyclohexaneto produceadipic acid in the'pr'esence of 'a'polyvalent heavy metal catalystselected from the group consisting of carboxylates of cobalt, manganeseand cyclohexanone reaction' initiator and both cobalt and manganese. theimprovement which comprises effecting said oxidation in a solution ofcyclohexane in a $01- A vent consisting essentially of acetone, theproportion of acetone in said solution being between about 10 and aboutpercent by weight.

4. In a process for the liquid-phase oxidation of cyclohexane to produceadipic acid in the presence of a polyvalent heavy metal catalystselected from the group consisting of carboxylates of cobalt, manganeseand both cobalt and manganese, at a temperature between about C. andabout 140 0., oxygen partial pressure between about 100 and about 300 p.s. i. g. and in,

the presence of a cyclohexanone initiator, the improvement whichcomprises efiecting said oxidation in a solution of cyclohexane in asolvent consisting essentially of acetone, the proportion of acetone insaid solution being between about 10 and about 70 percent by Weight.

' 5. A process for the oxidation of cyclohexane to produce adipic acid,which process comprises subjecting cyclohexane and a solvent consistingessentially of acetone in proportions between about 10 and about 70percent by weight, based on bothcyclohexane and acetone, to treatmentwith oxygen at a partial pressure between about 150 and about 250 p. s.i. g. at a temperature between about C. and about C. in the presence ofan ,adipate of a polyvalent heavy metal selected from the classconsisting of cobalt and cyclohexanone reaction initiator, manganese andboth manganese and cobalt, and thereafter separating adipic acid fromthe-reaction mixture.

6. A process for the oxidation of cyclohexane to produce adipic acid,which process comprises subjecting cyclohexane and a solvent consistingessentially of acetone in proportions between about 10, and about 70percent by weight, based on both cyclohexane and acetone, to treatmentganese and both manganese and cobalt, and

initially present cyclohexanone in an amount between about 0.1 and about1.0 percent by weight, based on cyclohexane, and thereafter separatingadipic acid from the reaction mixture.

' FRANCIST. WADSWORTH.-

REFERENCES CITED The following references'are of record in the file ofthis patent:

UNITED STATES PATENTS I Date Number Name 2,005,183 Flemming et a1. June18, 1935 2,223,493 Loder -1. Dec. 3, 1940 Drossbach June 9, 1942

1. IN A PROCESS FOR THE LIQUID-PHASE OXIDATION OF A LIQUID CYCLOALKANECONTAINING 4 TO 6 CARBON ATOMS, INCLUSIVE, IN THE RING TO PRODUCE ANALKANE DICARBOXYLIC ACID IN THE PRESENCE OF A POLYVALENT HEAVY METALCATALYST AND CYCLOHEXANONE REACTION INITIATOR, THE IMPROVEMENT WHICHCOMPRISES EFFECTING SAID OXIDATION IN A SOLUTION OF SAID CYCLOALKANE INA SOLVENT CONSISTING ESSENTIALLY OF ACETONE, THE PROPORTION OF ACETONEIN SAID SOLUTION BEING BETWEEN ABOUT 10 AND 70 PERCENT BY WEIGHT.